Factors influencing the gas bubble evolution and the cristobalite formation in quartz glass Cz crucibles for Czochralski growth of silicon crystals

•Investigation of gas bubble evolution and Crs formation on SiO2 crucibles by VBT.•Holding time increases bubble growth in natural SiO2 more than in synthetic SiO2.•Two Crs formation mechanisms depending on contact with/without Si are distinguished.•Crs thickness and covering increases with holding time. Long-term Czochralski (Cz) silicon crystallization processes like multi-pulling demand high qualities and performances of fused quartz crucibles. Crucial issues are the gas bubble evolution and cristobalite (Crs) formation within the bulk and on the inner crucible surfaces. Here, crucibles by four suppliers were investigated using vacuum bake-out tests (VBT), for which crucible samples are heat-treated under vacuum at 1450 °C for different holding times with and without direct Si contact. An improved data analysis showed that the bubbles in all crucibles grow with process time; however, the expansion is more pronounced in the bulk material than in the critical surface-near region. Further, we observed that the final bubble size is higher in natural than in synthetic SiO2 material. Crs formation could be observed at all crucibles' surfaces, distinguishable into brownish Crs at sites with Si contact and white Crs without Si contact. The resulting Crs layer thickness and the surface covering increased with longer holding times; however, too thick layers could cause chipping. Further, the observed Crs growth rate is different for all crucible types. Finally, the crucibles were evaluated for their highest application potential for long-term Cz experiments.